It is well known in the multiple ratio transmission art that synchronizer mechanisms may be used to reduce shift time of all or some of the transmission gear ratios. It is also known that the shift effort required by a vehicle operator, i.e., force applied to a shift lever, may be reduced by use of synchronizer mechanisms of the self-energizing type. Since operator shift effort generally increases with vehicle size, synchronizer mechanisms of the self-energizing type are especially important for heavy duty trucks. Prior art examples of such mechanisms may be seen by reference to U.S. Pat. Nos. 2,410,511; 2,896,760; 3,548,983; 4,413,715; 4,836,348; and 4,869,353 which are incorporated herein by reference.
The synchronizer mechanisms of the above patents include friction and jaw members for respectively synchronizing and positive clutching a gear to a shaft; blockers engaged in response to a pre-energizer effecting initial engagement of the friction members in response to initial engaging movement of one of the jaw members by a shift force, the blockers being operative to prevent asynchronous engagement of the jaw members and to transmit the shift force to the friction members to increase synchronizing torque thereof; and self-energizing ramps reacting the torque to provide an additional force in the direction of and additive to the shift force for further increasing the synchronizing torque of the friction members.
The structure of the synchronizer mechanisms in these patents differs substantially from the structure of pin-type synchronizer mechanisms. Due, at least in part, to these structural differences, it has been difficult to provide pin-type synchronizer mechanisms with the self-energizing feature mentioned above.
Further, while the synchronizer mechanisms of these patents may well have reduced shift time and shift effort, they have not taken into account varying shift requirements for the whole transmission, i.e., lower speed ratio gears in general require more shift effort and/or time than do high gear speed ratios, and that down shifts in general require more effort and/or time than do upshifts.